Imaging lens and imaging device

ABSTRACT

An imaging lens is provided with: a first lens with negative power; a second lens with negative power; a third lens with positive power; and a fourth lens with positive power. The cemented fourth lens is formed from an object side lens with negative power and an image side lens with positive power. The thickness of a resin adhesive layer that bonds the object side lens and the image side lens is 20 μm or greater on the optical axis, and when Sg 1 H is the amount of sag in the image side lens surface of the object side lens and Sg 2 H is the amount of sag in the object side lens surface of the image side lens. The bonding operation is easy without damage occurring to the cemented surfaces, with a design that takes into account thickness of the resin adhesive layer; therefore various forms of aberration can be corrected.

This is a Continuation of application Ser. No. 15/139,646 filed Apr. 27,2016, which in turn is a Continuation of application Ser. No. 14/375,968filed Jul. 31, 2014, now U.S. Pat. No. 9,360,656, which in turn is aNational Phase of International Patent Application No. PCT/JP2013/001036filed Feb. 22, 2013, which claims the benefit of Japanese PatentApplication No. 2012-076319 filed Mar. 29, 2012. The disclosure of theprior applications is hereby incorporated by reference herein in theirentireties.

TECHNICAL FIELD

The present invention relates to: an imaging lens provided with, inorder from an object side, a first lens, a second lens, a third lens,and a fourth lens, the fourth lens being a cemented lens; and an imagingdevice equipped with the imaging lens.

BACKGROUND ART

There are known imaging lenses equipped with a cemented lens in order tocorrect various forms of aberration, such as chromatic aberration, witha small number of lenses. The imaging lens disclosed in Patent Document1 is configured from, in order from an object side to an image side: afirst lens having negative power, a second lens having negative power, athird lens having positive power, and a fourth lens having positivepower, the fourth lens being a cemented lens. In this document, thecemented surfaces of the two lens constituting the fourth lens, i.e.,the image side lens surface of the object side lens and the object sidelens surface of the image side lens constituting the fourth lens, areboth aspheric in shape.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP 2006-284620 A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The cemented lens is configured by cementing two lenses (an object sidelens and an image side lens) using an acrylic resin adhesive. In thecemented lens, the resin adhesive layer formed between the two lenses bythe resin adhesive should be formed extremely thin, and the thickness ofthe resin adhesive layer is commonly 5 to 10 μm. This is because whenthe resin adhesive layer is thicker, it has the negative effect ofcausing the field curvature in the tangential surface to shift to theplus side, in comparison with a simulation of the optical properties ofthe imaging lens during the designing.

A possible solution to satisfactorily correct various forms ofaberration is to fashion the image side lens surface of the object lensand the object side lens surface of the image side lens constituting thecemented lens into different aspheric shapes. However, when the shapescemented surfaces are different from each other and the resin adhesivelayer is thinned, there is a greater danger of these cemented surfacescoming in contact with each other during the bonding operation and thecemented surfaces being damaged. When the gap between the cementedsurfaces of the lenses is narrowed in order to thin the resin adhesivelayer, the resin adhesive does not fill in between the cementedsurfaces, and air bubbles sometimes remain between the object side lensand the image side lens.

In view of such matters, a problem of the present invention is toprovide a high-resolution imaging lens comprising four lenses includingan easily manufactured cemented lens.

Means to Solve the Problems

To solve the problem described above, an imaging lens of the presentinvention is characterized in comprising, in order from an object sideto an image side:

a first lens having negative power, a second lens having negative power,a third lens having positive power, and a fourth lens having positivepower;

the fourth lens being a cemented lens composed of an object side lenshaving negative power and an image side lens having positive power, andbeing provided with a resin adhesive layer bonding the object side lensand the image side lens together;

an image side lens surface of the object side lens and an object sidelens surface of the image side lens having different aspheric shapes;and

the following conditional expressions (1) and (2) being satisfied, whereD represents the thickness of the adhesive resin layer along an opticalaxis, Sg1H represents sag at height H in the effective diameter of theimage side lens surface of the object side lens in a directionorthogonal to the optical axis, and Sg2H represents sag in the objectside lens surface of the image side lens at height H.

20 μm≦D  (1)

Sg1H≦Sg2H  (2)

According to the present invention, the image side lens surface of theobject side lens and the object side lens surface of the image sidelens, which are the cemented surfaces of the two lenses constituting thecemented lens, have different aspheric shapes. As a result, it is easyto correct various forms of aberration such as chromatic aberrationusing the cemented lens, and the imaging lens can therefore be made highresolution. Because the conditional expressions (1) and (2) aresatisfied, it is possible to increase the thickness of the adhesiveresin layer between the image side lens surface of the object side lensand the object side lens surface of the image side lens which havedifferent aspheric shapes, or in other words, to widen that gap betweenthe cemented surfaces of the two lenses constituting the cemented lens.Therefore, it is possible to prevent or suppress instances in which thecemented surfaces come in contact with each other during the bondingoperation of bonding the two lenses, and the cemented surfaces aredamaged. Because of the wide gap between the cemented surfaces, theresin adhesive easily fills in between the cemented surfaces, and airbubbles can be prevented from remaining between the two lenses.Therefore, manufacturing the cemented lens is easy. Furthermore, theimaging lens can be designed with a gap of 20 μm or greater set inadvance along the optical axis between the image side lens surface ofthe object side lens and the object side lens surface of the image sidelens constituting the cemented lens, it is therefore possible to designthe imaging lens while accounting for plus-side shifting of the fieldcurvature in the tangential surface, and plus-side shifting of the fieldcurvature can be suppressed by the design. The amount of sag is thedistance along the optical axis from a reference plane to a lens surfaceat height H in the effective diameter in a direction orthogonal to theoptical axis, the reference plane being a flat plane orthogonal to theoptical axis and including the point of intersection between the lenssurface and the optical axis. Furthermore, in the imaging lens of thepresent invention, it is possible to prevent or suppress the occurrenceof focus misalignment between photographing using a visible light rayand photographing using a near infrared ray. Therefore, it is possibleto install the imaging lens in an imaging device or the like whichphotographs utilizing a visible light ray and also photographs utilizinglight rays in the range of 800 nm to 1100 nm, for example, such as anear infrared ray including a wavelength of 850 nm. A visible light rayis a light ray with a wavelength in the range of 400 nm or greater, toless than 700 nm.

In the present invention, the following conditional expression (3) ispreferably satisfied.

D≦100 μm  (3)

If so, plus-side shifting of the field curvature in the tangentialsurface, caused by widening of the gap between the object side lens andthe image side lens, can be accommodated to an extent at whichcorrection is still possible.

In the present invention, the following conditional expression (4) ispreferably satisfied, where f represents the focal point distance of theentire lens system, and Rs represents the radius of curvature of theimage side lens surface of the object side lens.

0.9≦Rs/f≦1.3  (4)

When Rs/f falls below the lower limit of conditional expression (4), thecurvature of the cemented surfaces becomes large; therefore, cementingwith the image side lens is no longer easy and the work of cementing thecemented lens becomes difficult. When the upper limit of conditionalexpression (4) is exceeded, it is difficult to correct chromaticaberration.

In the present invention, the following conditional expression (5) ispreferably satisfied, where f represents the focal point distance of theentire lens system, f41 represents the focal point distance of theobject side lens, and f42 represents the focal point distance of theimage side lens.

−3.0≦(f41/f42)/f≦−1.5  (5)

When (f41/f42)/f falls below the lower limit of conditional expression(5), it is difficult to achieve balance with axial chromatic aberrationand magnification chromatic aberration, leading to loss of resolution inthe peripheral portions of the image. When the upper limit ofconditional expression (5) is exceeded, it is difficult to correctchromatic aberration. The upper limit and lower limit of conditionalexpression (5) are values that take into account axial chromaticaberration and magnification chromatic aberration in cases of utilizinga near infrared ray in a range including an 850 nm wavelength forimaging, and in cases of utilizing a visible light ray, the lower limitis preferably −2.5.

To make the imaging lens a wide angle lens in the present invention,preferably, the first lens is a meniscus lens having a convex shape inthe object side lens surface, the object side lens surface of the secondlens has a concave shape, the third lens has a convex shape in theobject side lens surface, and conditional expression (6) below issatisfied, where R31 represents the radius of curvature of the objectside lens surface of the third lens and R32 represents the radius ofcurvature of the image side lens surface of the third lens.

R31≦|R32|  (6)

In this case, the imaging lens of the present invention can be a wideangle lens with a half angle of view of 80° or greater.

To satisfactorily correct chromatic aberration in the present invention,the first lens, second lens, and image side lens preferably have an Abbenumber of 40 or greater, and the third lens and object side lenspreferably have an Abbe number of 31 or less.

The imaging device of the present invention according to another aspectis characterized in comprising the imaging lens described above, and animage pick-up device arranged in a focal point position of the imaginglens.

According to the present invention, because the imaging lens can be madehigh resolution, the imaging device can be made high resolution byinstalling an image pick-up device having a large number of pixels.

The imaging device of the present invention according to another aspectis characterized in comprising the imaging lens described above, animage pick-up device arranged in the focal point position of the imaginglens, and an optical filter for transmitting a visible light ray and anear infrared ray in a band including a wavelength of 850 nm, theoptical filter being arranged either on the object side of the imaginglens or between the imaging lens and the image pick-up device.

According to the present invention, the imaging lens prevents orsuppresses the occurrence of focus misalignment between photographingusing a visible light ray and photographing using a light ray of apredetermined range within the infrared range. Therefore, it is easy toconfigure an imaging device that uses the imaging lens to capture imagesutilizing a near infrared ray and a visible light ray.

Effect of the Invention

According to the present invention, because the cemented surfaces of thetwo lenses constituting the cemented lens have different asphericshapes, it is easy to correct various forms of aberration such aschromatic aberration using the cemented lens, and the imaging lens canbe made high resolution. Because conditional expressions (1) and (2) aresatisfied, it is possible to prevent or suppress instances of thecemented surfaces coming in contact with each other and the cementedsurfaces being damaged during the bonding operation of bonding the twolenses. The resin adhesive easily fills in between the cementedsurfaces, and air bubbles can be prevented from remaining in between thetwo lenses. Therefore, manufacturing the cemented lens is easy.Furthermore, the imaging lens can be designed with a gap of 20 μm orgreater set in advance along the optical axis between the image sidelens surface of the object side lens and the object side lens surface ofthe image side lens constituting the cemented lens, and plus-sideshifting of the field curvature in the tangential surface can thereforebe suppressed by the design. According to the present invention, it ispossible to prevent or suppress the occurrence of focus misalignmentbetween photographing using a visible light ray and photographing usinga near infrared ray.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an imaging lens of Example 1 towhich the present invention is applied.

FIG. 2 is an explanatory diagram of the amount of sag.

FIG. 3A is a longitudinal aberration graph of the imaging lens of FIG.1.

FIG. 3B is lateral aberration graphs of the imaging lens of FIG. 1.

FIG. 3C is a field curvature graph of the imaging lens of FIG. 1.

FIG. 3D is a distortion aberration graph of the imaging lens of FIG. 1.

FIG. 4 is a spherical aberration graph of the imaging lens of FIG. 1.

FIG. 5 is a configuration diagram of an imaging lens of Example 2 towhich the present invention is applied.

FIG. 6A is a longitudinal aberration graph of the imaging lens of FIG.5.

FIG. 6B is lateral aberration graphs of the imaging lens of FIG. 5.

FIG. 6C is a field curvature graph of the imaging lens of FIG. 5.

FIG. 6D is a distortion aberration graph of the imaging lens of FIG. 5.

FIG. 7 is a spherical aberration graph of the imaging lens of FIG. 5.

FIG. 8 is a configuration diagram of an imaging lens of Example 3 towhich the present invention is applied.

FIG. 9A is a longitudinal aberration graph of the imaging lens of FIG.8.

FIG. 9B is lateral aberration graphs of the imaging lens of FIG. 8.

FIG. 9C is a field curvature graph of the imaging lens of FIG. 8.

FIG. 9D is a distortion aberration graph of the imaging lens of FIG. 8.

FIG. 10 is a spherical aberration graph of the imaging lens of FIG. 8.

FIG. 11 is a configuration diagram of an imaging lens of Example 4 towhich the present invention is applied.

FIG. 12A is a longitudinal aberration graph of the imaging lens of FIG.11.

FIG. 12B is lateral aberration graphs of the imaging lens of FIG. 11.

FIG. 12C is a field curvature graph of the imaging lens of FIG. 11.

FIG. 12D is a distortion aberration graph of the imaging lens of FIG.11.

FIG. 13 is a spherical aberration graph of the imaging lens of FIG. 11.

FIG. 14 is a configuration diagram of an imaging lens of Example 5 towhich the present invention is applied.

FIG. 15A is a longitudinal aberration graph of the imaging lens of FIG.14.

FIG. 15B is lateral aberration graphs of the imaging lens of FIG. 14.

FIG. 15C is a field curvature graph of the imaging lens of FIG. 14.

FIG. 15D is a distortion aberration graph of the imaging lens of FIG.14.

FIG. 16 is a spherical aberration graph of the imaging lens of FIG. 14.

FIG. 17 is an explanatory diagram of an imaging device equipped with animaging lens.

FIG. 18 is a configuration diagram of an imaging lens of ReferenceExample 1.

FIG. 19A is a longitudinal aberration graph of the imaging lens of FIG.18.

FIG. 19B is lateral aberration graphs of the imaging lens of FIG. 18.

FIG. 19C is a field curvature graph of the imaging lens of FIG. 18.

FIG. 19D is a distortion aberration graph of the imaging lens of FIG.18.

FIG. 20 is a configuration diagram of an imaging lens of ReferenceExample 2.

FIG. 21A is a longitudinal aberration graph of the imaging lens of FIG.20.

FIG. 21B is lateral aberration graphs of the imaging lens of FIG. 20.

FIG. 21C is a field curvature graph of the imaging lens of FIG. 20.

FIG. 21D is a distortion aberration graph of the imaging lens of FIG.20.

FIG. 22 is a configuration diagram of an imaging lens of ReferenceExample 3.

FIG. 23A is a longitudinal aberration graph of the imaging lens of FIG.22.

FIG. 23B is lateral aberration graphs of the imaging lens of FIG. 22.

FIG. 23C is a field curvature graph of the imaging lens of FIG. 22.

FIG. 23D is a distortion aberration graph of the imaging lens of FIG.22.

MODE FOR CARRYING OUT THE INVENTION

An imaging lens to which the present invention is applied is describedbelow with reference to the drawings.

Example 1

FIG. 1 is a configuration diagram (light ray diagram) of an imaging lensof Example 1. An imaging lens 10 of the present example comprises, inorder from an object side to an image side, a first lens 11 havingnegative power, a second lens 12 having negative power, a third lens 13having positive power, and a fourth lens 14 having positive power. Adiaphragm 15 is arranged between the third lens 13 and the fourth lens14, and plate glass 16 is disposed on the image side of the fourth lens14. An image-forming surface I1 is in a separate position from the plateglass 16. The fourth lens 14 is a cemented lens comprising an objectside lens 17 having negative power and an image side lens 18 havingpositive power. The object side lens 17 and the image side lens 18 arebonded by a resin adhesive, and a resin adhesive layer B1 is formedbetween the object side lens 17 and the image side lens 18.

In the first lens 11, an object side lens surface 11 a is a meniscuslens protruding toward the object side. The object side lens surface 11a and an image side lens surface 11 b of the first lens 11 both havepositive curvature.

In the second lens 12, an object side lens surface 12 a has negativecurvature, and an image side lens surface 12 b has positive curvature.Therefore, the object side lens surface 12 a has a concave curvedportion that caves to the image side along the optical axis L1, and theimage side lens surface 12 b has a concave curved portion that caves tothe object side along the optical axis L1. The object side lens surface12 a and the image side lens surface 12 b are aspheric in shape.

In the third lens 13, an object side lens surface 13 a has positivecurvature, and an image side lens surface 13 b has positive curvature.Therefore, the object side lens surface 13 a has a convex curved portionthat protrudes to the object side along the optical axis L1, and theimage side lens surface 13 b has a convex curved portion that protrudesto the image side along the optical axis L1. The object side lenssurface 13 a and the image side lens surface 13 b of the third lens 13are aspheric in shape.

In an object side lens 17 of the fourth lens 14, an object side lenssurface 17 a has positive curvature, and an image side lens surface 17 bhas positive curvature. Therefore, the object side lens surface 17 a hasa convex curved portion that protrudes to the object side along theoptical axis L1, and the image side lens surface 17 b has a concavecurved portion that caves to the object side along the optical axis L1.The object side lens surface 17 a and the image side lens surface 17 bof the object side lens 17 are aspheric in shape.

In the image side lens 18 of the fourth lens 14, an object side lenssurface 18 a has positive curvature, and an image side lens surface 18 bhas negative curvature. Therefore, the object side lens surface 18 a hasa convex curved portion that protrudes to the object side along theoptical axis L1, and the image side lens surface 18 b has a convexcurved portion that protrudes to the image side along the optical axisL1. The object side lens surface 18 a and the image side lens surface 18b of the image side lens 18 are aspheric in shape.

The image side lens surface 17 b of the object side lens 17 and theobject side lens surface 18 a of the image side lens 18, whichconstitute the cemented surfaces of the object side lens 17 and theimage side lens 18, have different aspheric shapes. When D is thethickness of the resin adhesive layer B1 on the optical axis L1, Sg1H isthe amount of sag in the image side lens surface 17 b of the object sidelens 17 at height H in the effective diameter of the image side lenssurface 17 b of the object side lens 17 in a direction orthogonal to theoptical axis L1, and Sg2H is the amount of sag in the object side lenssurface 18 a of the image side lens 18 at height H, then the imaginglens 10 of the present example satisfies the conditional expressions (1)and (2) below. The amount of sag is the distance along the optical axisL1 from a reference plane to a lens surface at height H in the effectivediameter of the image side lens surface 17 b of the object side lens 17in a direction orthogonal to the optical axis L1, the reference planebeing a flat plane orthogonal to the optical axis L1 and including thepoint of intersection between the lens surface and the optical axis L1.FIG. 2 is an explanatory diagram of the amount of sag, wherein S1indicates a reference plane relative to the image side lens surface 17 bof the object side lens 17, and S2 indicates a reference plane relativeto the object side lens surface 18 a of the image side lens 18.

20 μm≦D  (1)

Sg1H≦Sg2H  (2)

The conditional expressions (1) and (2) stipulate the thickness of theresin adhesive layer B1 between the image side lens surface 17 b of theobject side lens 17 and the object side lens surface 18 a of the imageside lens 18 which have different aspheric shapes, or in other words,the gap between the image side lens surface 17 b of the object side lens17 and the object side lens surface 18 a of the image side lens 18,which are the cemented surfaces of the two lenses constituting thecemented lens.

Because the imaging lens 10 of the present example satisfies theconditional expressions (1) and (2), the gap between the image side lenssurface 17 b of the object side lens 17 and the object side lens surface18 a of the image side lens 18 can be enlarged. Therefore, during thebonding operation of bonding the object side lens 17 and the image sidelens 18, it is possible to prevent or suppress contact between the imageside lens surface 17 b of the object side lens 17 and the object sidelens surface 18 a of the image side lens 18, as well as any damage thatmay occur on these lens surfaces. Because there is a large gap betweenthe image side lens surface 17 b of the object side lens 17 and theobject side lens surface 18 a of the image side lens 18, the resinadhesive easily fills in between the lens surfaces, and air bubbles canbe prevented from remaining in between the two lenses.

The imaging lens 10 of the present example satisfies the followingconditional expression (3).

D≦100 μm  (3)

The purpose of conditional expression (3) is to suppress the increase inthe plus-side shift of the field curvature in a tangential surface. Whenthe upper limit of conditional expression (3) is exceeded, the plus-sideshift of the field curvature becomes larger and difficult to correct. Inthe present example, because D is equal to 20 μm, the plus-side shift ofthe field of curvature in the tangential surface can be corrected by thedesign.

Furthermore, when Rs is the radius of curvature of the image side lenssurface 17 b of the object side lens 17 and f is the focal pointdistance of the entire lens system, the imaging lens 10 of the presentexample satisfies the following conditional expression (4).

0.9≦Rs/f≦1.3  (4)

When Rs/f falls below the lower limit of conditional expression (4), thecurvature of the image side lens surface 17 b of the object side lens 17becomes large; therefore, cementing with the image side lens 18 is nolonger easy and the work of cementing the cemented lens becomesdifficult. When the upper limit of conditional expression (4) isexceeded, it is difficult to correct chromatic aberration. Because Rs/fis equal to 1.077 in the present example, it is easy to cement thecemented lens and chromatic aberration is corrected satisfactorily.

When f is the focal point distance of the entire lens system, f41 is thefocal point distance of the object side lens 17, and f42 is the focalpoint distance of the image side lens 18, the imaging lens 10 of thepresent example satisfies the following conditional expression (5).

−3.0≦(f41/f42)/f≦−1.5  (5)

When (f41/f42)/f falls below the lower limit of conditional expression(5), it is difficult to achieve balance with axial chromatic aberrationand magnification chromatic aberration, leading to loss of resolution inthe peripheral portions of the image. When the upper limit ofconditional expression (5) is exceeded, it is difficult to correctchromatic aberration. Because (f41/f42)/f is equal to −1.54 in thepresent example, the decrease in resolution can be suppressed, andchromatic aberration is corrected satisfactorily.

In the imaging lens 10 of the present example, when R31 is the radius ofcurvature of the object side lens surface 13 a of the third lens 13 andR32 is the radius of curvature of the image side lens surface 13 b ofthe third lens 13, R31 is equal to 3.573, R32 is equal to −5.766, andthe following conditional expression (6) is satisfied.

R31≦|R32|  (6)

In the imaging lens 10 of the present example, the Abbe number of thefirst lens 11, the second lens 12, and the image side lens 18 is 40 orgreater, and the Abbe number of the third lens 13 and the object sidelens 17 is 31 or less, whereby chromatic aberration is corrected.

When the F number of the imaging lens 10 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=99.4°

L=16.089 mm

When f represents the focal point distance of the entire lens system, f1represents the focal point distance of the first lens 11, f2 representsthe focal point distance of the second lens 12, f3 represents the focalpoint distance of the third lens 13, f4 represents the focal pointdistance of the fourth lens 14, f41 represents the focal point distanceof the object side lens 17, and f42 represents the focal point distanceof the image side lens 18, these values are as follows.

f=1.155 mm

f1=−8.193 mm

f2=−2.685 mm

f3=4.126 mm

f4=3.275 mm

f41=−3.351 mm

f42=1.885 mm

Next, table 1A shows lens data of the lens surfaces of the imaging lens10. In table 1A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 15, and surfaces 12 and 13 are the objectside glass surface and the image side glass surface of the plate glass16. Radius of curvature and gap are in units of millimeters. The valuesof Nd (refractive index) and νd (Abbe number) of surface 10 representvalues of the resin adhesive layer B1.

TABLE 1A Nd Vd Radius of (ref. (Abbe Surface Curvature Gap index) no.)1  17.158 1.000 1.77250 49.6 2  4.506 2.903 3* −56.607 1.415 1.5346156.0 4* 1.485 1.595 5* 3.573 2.087 1.58246 30.1 6* −5.766 0.866 7 infinity 0.923 8* 3.465 0.500 1.63494 24.0 9* 1.244 0.020 1.50000 50.010*  1.251 2.107 1.53461 56.0 11*  −2.145 1.000 12  infinity 0.6001.51680 64.2 13  infinity 1.074

Next, table 1B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 1B as well.

TABLE 1B 3rd 4th 5th 6th 8th 9th 10th 11th surface surface surfacesurface surface surface surface surface K −2.84625E+01 −1.40499E+00−5.08590E+00   0.00000E+00   1.31742E+00 −5.22053E−01 −5.18954E−01−5.07127E−01 A4 −7.73159E−04   9.48358E−03   1.29842E−02   1.24404E−02−1.27224E−02   2.05512E−03   1.55213E−02   2.38843E−02 A6   8.83607E−06  8.23544E−04   7.37044E−04 −2.28103E−03   1.37903E−03 −2.12211E−02−2.25983E−02 −2.51814E−03 A8   8.27198E−07   2.00365E−04 −8.09568E−05  9.57643E−04   0.00000E+00 −5.63452E−03 −8.00738E−03   1.41188E−03 A10−2.49701E−08 −3.23758E−05   1.68861E−06 −9.26933E−05   0.00000E+00  4.54812E−03   4.55649E−03 −2.09677E−04 A22   0.00000E+00   0.00000E+00  2.05962E−06   0.00000E+00   0.00000E+00 −9.87494E−04 −7.63457E−04  3.07858E−05 A14   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   1.16261E−05A16   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00

The aspheric shape employed for the lens surfaces is expressed by thefollowing formula, wherein Y is the amount of sag, c is the inverse ofthe radius of curvature, K is the conical coefficient, h is the heightof the light ray, and A4, A6, A8, A10, A12, A14, and A16 are asphericcoefficients of the fourth degree, the sixth degree, the eighth degree,the tenth degree, the twelfth degree, the fourteenth degree, and thesixteenth degree, respectively.

$\begin{matrix}{{Y(h)} = {\frac{{ch}^{2}}{1 + \sqrt{1 - {\left( {K + 1} \right)c^{2}h^{2}}}} + {A_{4}h^{4}} + {A_{6}h^{6}} + {A_{8}h^{8}} + {A_{10}h^{10}} + {A_{12}h^{12}} + {A_{14}h^{14}} + {A_{16}h^{16}}}} & \left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\end{matrix}$

(Effects)

FIGS. 3A to 3D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 10. In the longitudinal aberration graph of FIG. 3A,the horizontal axis represents the position where the light ray crossesthe optical axis L1, and the vertical axis represents the height at thepupil radius. In the lateral aberration graphs of FIG. 3B, thehorizontal axes represent entrance pupil coordinates, and the verticalaxes represent the amount of aberration. In FIGS. 3A and 3B, simulationresults are shown for a plurality of light rays of differentwavelengths. In the field curvature graph of FIG. 3C, the horizontalaxis represents distance in the direction of the optical axis L1, andthe vertical axis represents the height of the image. In FIG. 3C, Srepresents field curvature aberration in the sagittal plane, and Trepresents field curvature aberration in the tangential plane. In thedistortion aberration graph of FIG. 3D, the horizontal axis representsthe amount of image distortion, and the vertical axis represents theheight of the image.

According to the imaging lens 10 of the present example, axial chromaticaberration is satisfactorily corrected as shown in FIG. 3A. Colorbleeding is also suppressed as shown in FIG. 3B. Both axial chromaticaberration and magnification chromatic aberration are corrected in abalanced manner in the peripheral portions as well, as shown in FIGS. 3Aand 3B. Furthermore, according to the imaging lens 10 of the presentexample, field curvature is satisfactorily corrected as shown in FIG.3C. Therefore, the imaging lens 10 has high resolution.

In the present example, the imaging lens 10 is designed with a gap of 20μm or greater set in advance on the optical axis L1, between the imageside lens surface 17 b of the object side lens 17 and the object sidelens surface 18 a of the image side lens 18. Therefore, when the lens isbeing designed, it is possible to account for plus-side shifting of thefield curvature in the tangential plane, which occurs due to the resinadhesive layer B1 thickening. Therefore, according to the imaging lens10 of the present example, plus-side shifting of the field curvature inthe tangential plane is suppressed as shown in FIG. 3C.

Next, FIG. 4 is a spherical aberration graph of the imaging lens 10,wherein the solid line represents spherical aberration relative to alight ray with a wavelength of 588 nm (a visible light ray). The dashedline represents spherical aberration relative to a light ray with awavelength of 850 nm (a near infrared ray). The horizontal axis of thespherical aberration graph represents the position where the light raycrosses the optical axis, and the vertical axis represents the height ofthe pupil radius. In the imaging lens 10, spherical aberration relativeto a light ray with a wavelength of 850 nm is corrected as shown in FIG.4, and there is no need for adjusting the focus between photographingunder a visible light ray and photographing under a near infrared ray.In other words, in the imaging lens 10 of the present example, theoccurrence of focus misalignment is suppressed between photographingusing a visible light ray and photographing using a near infrared ray.In cases in which the fourth lens 14 is configured from a single lensthat is not a cemented lens, it is difficult to correct both sphericalaberration relative to a light ray with a wavelength of 588 nm (avisible light ray) and spherical aberration relative to a light ray witha wavelength of 850 nm (a near infrared ray) in a balanced manner, andalso to ensure that focus misalignment does not occur betweenphotographing using a visible light ray and photographing using a nearinfrared ray.

Example 2

FIG. 5 is a configuration diagram (light ray diagram) of an imaging lensof Example 2. An imaging lens 20 of the present example comprises, inorder from an object side to an image side, a first lens 21 havingnegative power, a second lens 22 having negative power, a third lens 23having positive power, and a fourth lens 24 having positive power, asshown in FIG. 5. A diaphragm 25 is disposed between the third lens 23and the fourth lens 24, and plate glass 26 is disposed on the image sideof the fourth lens 24. An image-forming surface 12 is in a separateposition from the plate glass 26. The fourth lens 24 is a cemented lenscomprising an object side lens 27 having negative power and an imageside lens 28 having positive power. The object side lens 27 and theimage side lens 28 are bonded by a resin adhesive, and a resin adhesivelayer B2 is formed between the object side lens 27 and the image sidelens 28. The shapes of the lenses constituting the imaging lens 20 ofthe present example are the same as the shapes of the lensescorresponding to the imaging lens 10 of Example 1, and descriptionsthereof are therefore omitted.

When the F number of the imaging lens 20 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=97.6°

L=15.598 mm

When f is the focal point distance of the entire lens system, f1 is thefocal point distance of the first lens 21, f2 is the focal pointdistance of the second lens 22, f3 is the focal point distance of thethird lens 23, f4 is the focal point distance of the fourth lens 24, f41is the focal point distance of the object side lens 27, and f42 is thefocal point distance of the image side lens 28, these values are asfollows.

f=1.141 mm

f1=−8.378 mm

f2=−2.600 mm

f3=4.060 mm

f4=3.199 mm

f41=−3.520 mm

f42=1.829 mm

In the imaging lens 20 of the present example, when D is the thicknessof the resin adhesive layer B2 on the optical axis L2, Sg1H is theamount of sag in the image side lens surface 27 b of the object sidelens 27 at height H in the effective diameter of the image side lenssurface 27 b of the object side lens 27 in a direction orthogonal to theoptical axis L2, Sg2H is the amount of sag in the object side lenssurface 28 a of the image side lens 28 at height H, Rs is the radius ofcurvature of the image side lens surface 27 b of the object side lens27, R31 is the radius of curvature of the object side lens surface 23 aof the third lens 23, and R32 is the radius of curvature of the imageside lens surface 23 b of the third lens 23, then the conditionalexpressions (1) to (6) given in the description of Example 1 aresatisfied, and the values of the conditional expressions (1) and (3) to(6) are as follows.

20 μm≦D=20 μm  (1)

Sg1H≦Sg2H  (2)

D=20 μm≦100 μm  (3)

0.9≦Rs/f=1.112≦1.3  (4)

−3.0≦(f41/f42)/f=−1.69≦−1.5  (5)

R31=3.428≦|R32|=|−5.958|  (6)

Furthermore, in the imaging lens 20 of the present example, the Abbenumber of the first lens 21, the second lens 22, and the image side lens28 is 40 or greater, and the Abbe number of the third lens 23 and theobject side lens 27 is 31 or less, whereby chromatic aberration iscorrected.

Next, table 2A shows lens data of the lens surfaces of the imaging lens20. In table 2A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 25, and surfaces 12 and 13 are the objectside glass surface and the image side glass surface of the plate glass26. Radius of curvature and gap are in units of millimeters. The valuesof Nd (refractive index) and νd (Abbe number) of the tenth surfacerepresent values of the resin adhesive layer B2.

TABLE 2A Nd Vd Radius of (ref. (Abbe Surface Curvature Gap index) no.)1  16.082 1.000 1.77250 49.6 2  4.490 2.831 3* −52.186 1.348 1.5346156.0 4* 1.441 1.594 5* 3.428 2.037 1.58246 30.1 6* −5.958 0.829 7 infinity 0.909 8* 3.388 0.500 1.63494 24.0 9* 1.269 0.020 1.50000 50.010*  1.270 1.785 1.53461 56.0 11*  −2.169 1.000 12  infinity 0.8001.51680 64.2 13  infinity 0.946

Next, table 2B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 2B as well.

TABLE 2B 3rd 4th 5th 6th 8th 9th 10th 11th surface surface surfacesurface surface surface surface surface K −4.85524E+01 −1.34758E+00−5.03141E+00   0.00000E+00   1.36928E+00 −4.83880E−01 −4.77306E−01−5.52365E−01 A4 −6.08537E−04   1.01062E−02   1.36480E−02   1.41031E−02−1.15999E−02   5.41293E−03   9.13101E−02   2.11256E−02 A6   1.09398E−05  6.68407E−04   6.11024E−04 −2.61724E−03   1.63819E−03 −1.93570E−02−1.66609E−02 −1.21540E−03 A8   3.28794E−07   1.40973E−04 −1.03327E−04  8.52922E−04   0.00000E+00 −4.66595E−03 −8.41125E−03   1.48351E−03 A10−1.20383E−08 −3.09290E−05   1.60209E−05 −7.04918E−05   0.00000E+00  4.64886E−03   5.56732E−03 −2.54428E−04 A12   0.00000E+00   0.00000E+00  1.74143E−06   0.00000E+00   0.00000E+00 −9.51682E−04 −8.11428E−04  2.89948E−05 A14   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   1.92218E−05A16   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00

(Effects)

FIGS. 6A to 6D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 20. According to the imaging lens 20, axial chromaticaberration is satisfactorily corrected as shown in FIG. 6A. Colorbleeding is also suppressed as shown in FIG. 6B. Both axial chromaticaberration and magnification chromatic aberration are corrected in abalanced manner in the peripheral portions as well, as shown in FIGS. 6Aand 6B. Furthermore, according to the imaging lens 20 of the presentexample, field curvature is satisfactorily corrected as shown in FIG.6C. Therefore, the imaging lens 20 has high resolution.

In the present example, the imaging lens 20 is designed with a gap of 20μm or greater set in advance on the optical axis L2, between the imageside lens surface 27 b of the object side lens 27 and the object sidelens surface 28 a of the image side lens 28. Therefore, when the lens isbeing designed, it is possible to account for plus-side shifting of thefield curvature in the tangential plane, which occurs due to the resinadhesive layer B2 thickening. Therefore, according to the imaging lens20 of the present example, plus-side shifting of the field curvature inthe tangential plane is suppressed as shown in FIG. 6C.

Next, FIG. 7 is a spherical aberration graph of the imaging lens 20,wherein the solid line represents spherical aberration relative to alight ray with a wavelength of 588 nm (a visible light ray). The dashedline represents spherical aberration relative to a light ray with awavelength of 850 nm (a near infrared ray). The horizontal axis of thespherical aberration graph represents the position where the light raycrosses the optical axis, and the vertical axis represents the height ofthe pupil radius. In the imaging lens 20, spherical aberration relativeto a light ray with a wavelength of 850 nm is corrected as shown in FIG.7, and there is no need for adjusting the focus between photographingunder a visible light ray and photographing under a near infrared ray.In other words, in the imaging lens 20 of the present example, theoccurrence of focus misalignment is suppressed between photographingusing a visible light ray and photographing using a near infrared ray.

Example 3

FIG. 8 is a configuration diagram (light ray diagram) of an imaging lensof Example 3. An imaging lens 30 of the present example comprises, inorder from an object side to an image side, a first lens 31 havingnegative power, a second lens 32 having negative power, a third lens 33having positive power, and a fourth lens 34 having positive power, asshown in FIG. 8. A diaphragm 35 is disposed between the third lens 33and the fourth lens 34, and plate glass 36 is disposed on the image sideof the fourth lens 34. An image-forming surface 13 is in a separateposition from the plate glass 36. The fourth lens 34 is a cemented lenscomprising an object side lens 37 having negative power and an imageside lens 38 having positive power. The object side lens 37 and theimage side lens 38 are bonded by a resin adhesive, and a resin adhesivelayer B3 is formed between the object side lens 37 and the image sidelens 38. The shapes of the lenses constituting the imaging lens 30 ofthe present example are the same as the shapes of the lensescorresponding to the imaging lens 10 of Example 1, and descriptionsthereof are therefore omitted.

When the F number of the imaging lens 30 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=96.0°

L=12.637 mm

When f represents the focal point distance of the entire lens system, f1represents the focal point distance of the first lens 31, f2 representsthe focal point distance of the second lens 32, f3 represents the focalpoint distance of the third lens 33, f4 represents the focal pointdistance of the fourth lens 34, f41 represents the focal point distanceof the object side lens 37, and f42 represents the focal point distanceof the image side lens 38 these values are as follows.

f=0.847 mm

f1=−5.553 mm

f2=−1.712 mm

f3=2.742 mm

f4=2.317 mm

f41=−2.670 mm

f42=1.493 mm

In the imaging lens 30 of the present example, when D represents thethickness of the resin adhesive layer B3 on the optical axis L3, Sg1Hrepresents the amount of sag in the image side lens surface 37 b of theobject side lens 37 at height H in the effective diameter of the imageside lens surface 37 b of the object side lens 37 in a directionorthogonal to the optical axis L3, Sg2H represents the amount of sag inthe object side lens surface 38 a of the image side lens 38 at height H,Rs represents the radius of curvature of the image side lens surface 37b of the object side lens 37, R31 represents the radius of curvature ofthe object side lens surface 33 a of the third lens 33, and R32represents the radius of curvature of the image side lens surface 33 bof the third lens 33, then the conditional expressions (1) to (6) givenin the description of Example 1 are satisfied, and the values of theconditional expressions (1) and (3) to (6) are as follows.

20 μm≦D=20 μm  (1)

Sg1H≦Sg2H  (2)

D=20 μm≦100 μm  (3)

0.9≦Rs/f=1.103≦1.3  (4)

−3.0≦(f41/f42)/f=−2.11≦−1.5  (5)

R31=1.824≦|R32|=|−8.292|  (6)

Furthermore, in the imaging lens 30 of the present example, the Abbenumber of the first lens 31, the second lens 32, and the image side lens38 is 40 or greater, and the Abbe number of the third lens 33 and theobject side lens 37 is 31 or less, whereby chromatic aberration iscorrected.

Next, table 3A shows lens data of the lens surfaces of the imaging lens30. In table 3A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 35, and surfaces 12 and 13 are the objectside glass surface and the image side glass surface of the plate glass36. Radius of curvature and gap are in units of millimeters. The valuesof Nd (refractive index) and νd (Abbe number) of the tenth surfacerepresent values of the resin adhesive layer B3.

TABLE 3A Nd Vd Radius of (ref. (Abbe Surface Curvature Gap index) no.)1  15.167 1.000 1.77250 49.6 2  3.248 2.137 3* −82.115 1.192 1.5346156.0 4* 0.930 0.833 5* 1.824 1.754 1.58246 30.1 6* −8.292 1.047 7 infinity 0.267 8* 2.522 0.500 1.63232 23.3 9* 0.934 0.020 1.50000 50.010*  0.985 1.881 1.53461 56.0 11*  −1.407 1.000 12  infinity 0.3001.51680 64.2 13  infinity 0.707

Next, table 3B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 3B as well.

TABLE 3B 3rd 4th 5th 6th 8th 9th 10th 11th surface surface surfacesurface surface surface surface surface K −3.60256E+0 −1.06928E+00−1.33964E+00   0.00000E+00   2.70264E+00 −4.4838 7E−01 −8.31760E−01−5.28763E−01 A4 −1.66270E−03   2.14019E−02   3.98212E−02   4.99316E−02−6.76570E−02 −6.46831E02   1.97069E−01   6.63000E−02 A6 −2.50310E−05−1.35178E−02 −1.87024E−03 −2.94229E−02   0.00000E+00 −6.49574E−02−2.33004E−01 −3.07803E−02 A8   4.90298E−06   3.07720E−03 −1.72035E−03  1.41316E−02   0.00000E+00 −1.82272E−01 −5.31866E−02   2.74275E−02 A10−3.49239E−07 −4.65455E−04   8.49190E−04 −2.20487E−03   0.00000E+00  2.14111E−01   8.43919E−02 −8.24114E−03 A12   0.00000E+00   0.00000E+00−6.45946E−05   0.00000E+00   0.00000E+00 −7.23247E−02   0.00000E+00  1.10075E−03 A14   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00 −2.46844E−04 A16  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00

(Effects)

FIGS. 9A to 9D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 30. According to the imaging lens 30, axial chromaticaberration is satisfactorily corrected as shown in FIG. 9A. Colorbleeding is also suppressed as shown in FIG. 9B. Both axial chromaticaberration and magnification chromatic aberration are corrected in abalanced manner in the peripheral portions as well, as shown in FIGS. 9Aand 9B. Furthermore, according to the imaging lens 30 of the presentexample, field curvature is satisfactorily corrected as shown in FIG.9C. Therefore, the imaging lens 30 has high resolution.

In the present example, the imaging lens 30 is designed with a gap of 20μm or greater set in advance on the optical axis L3, between the imageside lens surface 37 b of the object side lens 37 and the object sidelens surface 38 a of the image side lens 38. Therefore, when the lens isbeing designed, it is possible to account for plus-side shifting of thefield curvature in the tangential plane, which occurs due to the resinadhesive layer B3 thickening. Therefore, according to the imaging lens30 of the present example, plus-side shifting of the field curvature inthe tangential plane is suppressed as shown in FIG. 9C.

Next, FIG. 10 is a spherical aberration graph of the imaging lens 30,wherein the solid line represents spherical aberration relative to alight ray with a wavelength of 588 nm (a visible light ray). The dashedline represents spherical aberration relative to a light ray with awavelength of 850 nm (a near infrared ray). The horizontal axis of thespherical aberration graph represents the position where the light raycrosses the optical axis, and the vertical axis represents the height ofthe pupil radius. In the imaging lens 30, spherical aberration relativeto a light ray with a wavelength of 850 nm is corrected as shown in FIG.10, and there is no need for adjusting the focus between photographingunder a visible light ray and photographing under a near infrared ray.In other words, in the imaging lens 30 of the present example, theoccurrence of focus misalignment is suppressed between photographingusing a visible light ray and photographing using a near infrared ray.

Example 4

FIG. 11 is a configuration diagram (light ray diagram) of an imaginglens of Example 4. An imaging lens 40 of the present example comprises,in order from an object side to an image side, a first lens 41 havingnegative power, a second lens 42 having negative power, a third lens 43having positive power, and a fourth lens 44 having positive power, asshown in FIG. 8. A diaphragm 45 is disposed between the third lens 43and the fourth lens 44, and plate glass 46 is disposed on the image sideof the fourth lens 44. An image-forming surface 14 is in a separateposition from the plate glass 46. The fourth lens 44 is a cemented lenscomprising an object side lens 47 having negative power and an imageside lens 48 having positive power. The object side lens 47 and theimage side lens 48 are bonded by a resin adhesive, and a resin adhesivelayer B4 is formed between the object side lens 47 and the image sidelens 48. The shapes of the lenses constituting the imaging lens 40 ofthe present example are the same as the shapes of the lensescorresponding to the imaging lens 10 of Example 1, and descriptionsthereof are therefore omitted.

When the F number of the imaging lens 40 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=96.0°

L=13.514 mm

When f represents the focal point distance of the entire lens system, f1represents the focal point distance of the first lens 41, f2 representsthe focal point distance of the second lens 42, f3 represents the focalpoint distance of the third lens 43, f4 represents the focal pointdistance of the fourth lens 44, f41 represents the focal point distanceof the object side lens 47, and f42 represents the focal point distanceof the image side lens 48, these values are as follows.

f=0.994 mm

f1=−8.279 mm

f2=−1.785 mm

f3=2.929 mm

f4=2.394 mm

f41=−3.114 mm

f42=1.479 mm

In the imaging lens 40 of the present example, when D represents thethickness of the resin adhesive layer B4 on the optical axis L4, Sg1Hrepresents the amount of sag in the image side lens surface 47 b of theobject side lens 47 at height H in the effective diameter of the imageside lens surface 47 b of the object side lens 47 in a directionorthogonal to the optical axis L4, Sg2H represents the amount of sag inthe object side lens surface 48 a of the image side lens 48 at height H,Rs represents the radius of curvature of the image side lens surface 47b of the object side lens 47, R31 represents the radius of curvature ofthe object side lens surface 43 a of the third lens 43, and R32represents the radius of curvature of the image side lens surface 43 bof the third lens 43, then the conditional expressions (1) to (6) givenin the description of Example 1 are satisfied, and the values of theconditional expressions (1) and (3) to (6) are as follows.

20 μm≦D=20 μm  (1)

Sg1H≦Sg2H  (2)

D=20 μm≦100 μm  (3)

0.9≦Rs/f=1.189≦1.3  (4)

−3.0≦(f41/f42)/f=−2.12≦−1.5  (5)

R31=2.115≦|R32|=|−5.863|  (6)

Furthermore, in the imaging lens 40 of the present example, the Abbenumber of the first lens 41, the second lens 42, and the image side lens48 is 40 or greater, and the Abbe number of the third lens 43 and theobject side lens 47 is 31 or less, whereby chromatic aberration iscorrected.

Next, table 4A shows lens data of the lens surfaces of the imaging lens40. In table 4A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 45, and surfaces 12 and 13 are the objectside glass surface and the image side glass surface of the plate glass46. Radius of curvature and gap are in units of millimeters. The valuesof Nd (refractive index) and νd (Abbe number) of the tenth surfacerepresent values of the resin adhesive layer B4.

TABLE 4A Radius of Nd (ref. Vd (Abbe Surface Curvature Gap index) no.)1  19.042 1.000 1.58913 61.3 2  3.807 2.812 3* −11.513 1.548 1.5441056.1 4* 1.111 0.472 5* 2.115 1.930 1.58250 30.2 6* −5.863 0.929 7 infinity 0.371 8* 3.389 0.500 1.63980 23.3 9* 1.182 0.020 1.51313 53.910*  1.135 1.489 1.54410 56.1 11*  −1.487 1.000 12  infinity 0.3001.51680 64.2 13  infinity 1.143

Next, table 4B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 4B as well.

TABLE 4B 3rd 4th 5th 6th 8th 9th 10th 11th surface surface surfacesurface surface surface surface surface K   0.00000E+00 −1.14072E+00−1.65827E+00 −6.16240E+00   3.81816E+00 −3.72777E−01 −4.73549E−01−4.35515E−01 A4 −1.60230E−03   1.77641E−02   3.73407E−02   4.78862E−02−4.94012E−02 −1.04207E−02 −6.80388E−02   4.43708E−02 A6   6.88899E−06−1.55775E−02 −3.26048E−03 −1.99747E−02   1.07795E−01 −1.42219E−01−6.47585E−02 −1.90538E−02 A8   8.41573E−06   2.55153E−03 −1.80394E−03  1.50700E−03 −3.28112E−01   1.30746E−01 −1.30859E−02   2.58744E−02 A10  6.48226E−08 −2.92172E−05   9.45624E−04   1.79524E−02   4.00692E−01  3.22870E−02   1.30450E−02 −8.50588E−03 A12 −1.39532E−08   5.56951E−06−4.05919E−05 −1.36560E−02 −9.62778E−02   1.66066E−02   1.64851E−02  1.57286E−03 A14   0.00000E+00   0.00000E+00   0.00000E+00  4.66002E−03 −1.32539E−01   3.12449E−03   1.03073E−02 −7.60301E−05 A16  0.00000E+00   0.00000E+00   0.00000E+00 −6.74695E−04   6.80049E−02−9.02035E−03 −1.04512E−02 −1.29595E−04

(Effects)

FIGS. 12A to 12D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 40. According to the imaging lens 40, axial chromaticaberration is satisfactorily corrected as shown in FIG. 12A. Colorbleeding is also suppressed as shown in FIG. 12B. Both axial chromaticaberration and magnification chromatic aberration are corrected in abalanced manner in the peripheral portions as well, as shown in FIGS.12A and 12B. Furthermore, according to the imaging lens 40 of thepresent example, field curvature is satisfactorily corrected as shown inFIG. 12C. Therefore, the imaging lens 40 has high resolution.

In the present example, the imaging lens 40 is designed with a gap of 20μm or greater set in advance on the optical axis L4, between the imageside lens surface 47 b of the object side lens 47 and the object sidelens surface 48 a of the image side lens 48. Therefore, when the lens isbeing designed, it is possible to account for plus-side shifting of thefield curvature in the tangential plane, which occurs due to the resinadhesive layer B4 thickening. Therefore, according to the imaging lens40 of the present example, plus-side shifting of the field curvature inthe tangential plane is suppressed as shown in FIG. 12C.

Next, FIG. 13 is a spherical aberration graph of the imaging lens 40,wherein the solid line represents spherical aberration relative to alight ray with a wavelength of 588 nm (a visible light ray). The dashedline represents spherical aberration relative to a light ray with awavelength of 850 nm (a near infrared ray). The horizontal axis of thespherical aberration graph represents the position where the light raycrosses the optical axis, and the vertical axis represents the height ofthe pupil radius. In the imaging lens 40, spherical aberration relativeto a light ray with a wavelength of 850 nm is corrected as shown in FIG.13, and there is no need for adjusting the focus between photographingunder a visible light ray and photographing under a near infrared ray.In other words, in the imaging lens 40 of the present example, theoccurrence of focus misalignment is suppressed between photographingusing a visible light ray and photographing using a near infrared ray.

Example 5

FIG. 14 is a configuration diagram (light ray diagram) of an imaginglens of Example 5. An imaging lens 50 of the present example comprises,in order from an object side to an image side, a first lens 51 havingnegative power, a second lens 52 having negative power, a third lens 53having positive power, and a fourth lens 54 having positive power, asshown in FIG. 14. A diaphragm 55 is disposed between the third lens 53and the fourth lens 54, and plate glass 56 is disposed on the image sideof the fourth lens 54. An image-forming surface 15 is in a separateposition from the plate glass 56. The fourth lens 54 is a cemented lenscomprising an object side lens 57 having negative power and an imageside lens 58 having positive power. The object side lens 57 and theimage side lens 58 are bonded by a resin adhesive, and a resin adhesivelayer B5 is formed between the object side lens 57 and the image sidelens 58. The shapes of the lenses constituting the imaging lens 50 ofthe present example are the same as the shapes of the lensescorresponding to the imaging lens 10 of Example 1, and descriptionsthereof are therefore omitted.

When the F number of the imaging lens 50 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=100.0°

L=19.664 mm

When f is the focal point distance of the entire lens system, f1 is thefocal point distance of the first lens 51, f2 is the focal pointdistance of the second lens 52, f3 is the focal point distance of thethird lens 53, f4 is the focal point distance of the fourth lens 54, f41is the focal point distance of the object side lens 57, and f42 is thefocal point distance of the image side lens 58, these values are asfollows.

f=1.248 mm

f1=−8.890 mm

f2=−2.602 mm

f3=4.265 mm

f4=3.481 mm

f41=−4.227 mm

f42=1.479 mm

In the imaging lens 50 of the present example, when D is the thicknessof the resin adhesive layer B5 on the optical axis L5, Sg1H is theamount of sag in the image side lens surface 57 b of the object sidelens 57 at height H in the effective diameter of the image side lenssurface 57 b of the object side lens 57 in a direction orthogonal to theoptical axis L5, Sg2H is the amount of sag in the object side lenssurface 58 a of the image side lens 58 at height H, Rs is the radius ofcurvature of the image side lens surface 57 b of the object side lens57, R31 is the radius of curvature of the object side lens surface 53 aof the third lens 53, and R32 is the radius of curvature of the imageside lens surface 53 b of the third lens 53, then the conditionalexpressions (1) to (6) given in the description of Example 1 aresatisfied, and the values of the conditional expressions (1) and (3) to(6) are as follows.

20 μm≦D=20 μm  (1)

Sg1H≦Sg2H  (2)

D=20 μm≦100 μm  (3)

0.9≦Rs/f=1.120≦1.3  (4)

−3.0≦(f41/f42)/f=−1.50≦−1.5  (5)

R31=2.828≦|R32|=|−13.176|  (6)

Furthermore, in the imaging lens 50 of the present example, the Abbenumber of the first lens 51, the second lens 52, and the image side lens58 is 40 or greater, and the Abbe number of the third lens 53 and theobject side lens 57 is 31 or less, whereby chromatic aberration iscorrected.

Next, table 5A shows lens data of the lens surfaces of the imaging lens50. In table 5A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 55, and surfaces 12 and 13 are the objectside glass surface and the image side glass surface of the plate glass56. Radius of curvature and gap are in units of millimeters. The valuesof Nd (refractive index) and νd (Abbe number) of the tenth surfacerepresent values of the resin adhesive layer B5.

TABLE 5A Nd Vd Radius of (ref. (Abbe Surface Curvature Gap index) no.)1  23.391 1.494 1.7725 49.6 2  5.161 3.317 3* −89.639 1.888 1.5346 56.274* 1.423 1.373 5* 2.828 2.729 1.5825 30.18 6* −13.176 1.471 7  infinity0.651 8* 3.582 0.820 1.63493 23.89 9* 1.398 0.020 1.5 50 10*  1.4093.038 1.5346 56.27 11*  −2.097 1.000 12  infinity 0.600 1.5168 64.2 13 infinity 1.263

Next, table 5B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 5B as well.

TABLE 5B 3rd 4th 5th 6th 8th 9th 10th 11th surface surface surfacesurface surface surface surface surface K   6.03211E+01 −1.09619E+00−1.54839E+00   0.00000E+00   1.98881E+00 −3.94577E−01 −1.02230E+00−5.74699E−01 A4 −6.38352E−04   5.25824E−03   1.12674E−02   1.36867E−02−1.69038E−02 −3.53157E−03   5.32513E−02   1.90393E−02 A6   3.34872E−06−1.58711E−03 −2.76736E−04 −3.62175E−03   0.00000E+00 −1.92894E−02−2.50742E−02 −3.09208E−03 A8   2.84477E−07   1.49809E−04 −7.57961E−05  8.49297E−04   0.00000E+00 −6.20294E−03 −2.79467E−03   1.24752E−03 A10−8.74143E−09 −8.75115E−06   1.91559E−05 −6.65457E−05   0.00000E+00  4.93769E−03   2.06775E−03 −1.89301E−04 A12   0.00000E+00   0.00000E+00−8.62848E−07   0.00000E+00   0.00000E+00 −9.98388E−04   0.00000E+00  1.45505E−05 A14   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00 −8.37640E−07 A16  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00

(Effects)

FIGS. 15A to 15D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 50. According to the imaging lens 50, axial chromaticaberration is satisfactorily corrected as shown in FIG. 15A. Colorbleeding is also suppressed as shown in FIG. 15B. Both axial chromaticaberration and magnification chromatic aberration are corrected in abalanced manner in the peripheral portions as well, as shown in FIGS.15A and 15B. Furthermore, according to the imaging lens 50 of thepresent example, field curvature is satisfactorily corrected as shown inFIG. 15C. Therefore, the imaging lens 50 has high resolution.

In the present example, the imaging lens 50 is designed with a gap of 20μm or greater set in advance on the optical axis L5, between the imageside lens surface 57 b of the object side lens 57 and the object sidelens surface 58 a of the image side lens 58. Therefore, when the lens isbeing designed, it is possible to account for plus-side shifting of thefield curvature in the tangential plane, which occurs due to the resinadhesive layer B5 thickening. Therefore, according to the imaging lens50 of the present example, plus-side shifting of the field curvature inthe tangential plane is suppressed as shown in FIG. 15C.

Next, FIG. 16 is a spherical aberration graph of the imaging lens 50,wherein the solid line represents spherical aberration relative to alight ray with a wavelength of 588 nm (a visible light ray). The dashedline represents spherical aberration relative to a light ray with awavelength of 850 nm (a near infrared ray). The horizontal axis of thespherical aberration graph represents the position where the light raycrosses the optical axis, and the vertical axis represents the height ofthe pupil radius. In the imaging lens 50, spherical aberration relativeto a light ray with a wavelength of 850 nm is corrected as shown in FIG.16, and there is no need for adjusting the focus between photographingunder a visible light ray and photographing under a near infrared ray.In other words, in the imaging lens 50 of the present example, theoccurrence of focus misalignment is suppressed between photographingusing a visible light ray and photographing using a near infrared ray.

Other Embodiments

In the image-capturing lenses 10 to 50 described above, the image sidelens surfaces (13 b, 23 b, 33 b, 43 b, 53 b) of the third lenses haveconvex curved portions that have negative curvature and protrudeprogressively farther toward the image side along the optical axis, butthese image side lens surfaces (13 b, 23 b, 33 b, 43 b, 53 b) may haveconcave curved portions that have positive curvature and caveprogressively farther toward the object side along the optical axis. Itis easy in this case as well to make the image-capturing lenses 10 to 50into wide angle lenses by satisfying conditional expression (6).

(Imaging Device)

FIG. 17 is an explanatory diagram of an imaging device equipped with animaging lens of the present invention. The imaging device 60 has animage pick-up device 61 in which a sensor surface 61 a is disposed onthe image-forming surface I1 (focal point position) of the imaging lens10, as shown in FIG. 17. The image pick-up device 61 is a CCD sensor ora CMOS sensor.

According to the present example, because the imaging lens has highresolution, the imaging device 60 can be made to have high resolution byemploying an image pick-up device with a high number of pixels as theimage pick-up device 61. The imaging device 60 herein can be equippedwith any of the imaging lenses 20 to 50 in the same manner as theimaging lens 10, in which case the same effects can be achieved.

The imaging device 60 can be made into an imaging device that utilizes anear infrared ray and a visible light ray by disposing an optical filter62, which transmits a visible light ray and a near infrared ray of arange including a wavelength of 850 nm and guides the light rays to theimaging lens 10, between the imaging lens 10 and the image pick-updevice 61, as shown by the double-dotted line in FIG. 17. Specifically,the imaging lens 10 prevents or suppresses the occurrence of focusmisalignment between photographing using a visible light ray andphotographing using a near infrared ray. Therefore, merely equipping theimaging device 60 with the optical filter 62 makes it possible toconfigure an imaging device that performs both imaging utilizing a nearinfrared ray including a wavelength of 850 nm, i.e. a light ray in arange of 800 nm to 1100 nm for example, and imaging utilizing a visiblelight ray, i.e. visible light with a wavelength of 400 nm to 700 nm. Theoccurrence of focus misalignment between photographing using a visiblelight ray and photographing using a near infrared ray is prevented orsuppressed in the imaging lenses 20 to 50 as well. Therefore, merelyequipping the imaging device 60 with the optical filter 62 makes itpossible to configure an imaging device that performs both imagingutilizing a near infrared ray including a wavelength of 850 nm andimaging utilizing a visible light ray, similar to cases of using theimaging lens 10. The optical filter 62 may be disposed on the objectsides of the imaging lenses 10 to 50.

Reference Example 1

Imaging lenses of Reference Examples 1 to 3 are described below withreference to FIGS. 18 to 23. The imaging lenses of Reference Examples 1to 3 have configurations similar to Examples 1 to 5, but the thicknessalong the optical axis of the resin adhesive layer bonding the twolenses constituting the cemented lens, i.e., the gap along the opticalaxis between the two lenses constituting the cemented lens, is less than20 μm.

FIG. 18 is a configuration diagram (light ray diagram) of an imaginglens of Reference Example 1. An imaging lens 70 of the present examplecomprises, in order from an object side to an image side, a first lens71 having negative power, a second lens 72 having negative power, athird lens 73 having positive power, and a fourth lens 74 havingpositive power, as shown in FIG. 18. A diaphragm 75 is disposed betweenthe third lens 73 and the fourth lens 74, and plate glass 76 is disposedon the image side of the fourth lens 74. An image-forming surface 17 isin a separate position from the plate glass 76. The fourth lens 74 is acemented lens comprising an object side lens 77 having negative powerand an image side lens 78 having positive power. An image side lenssurface 77 b of the object side lens 77 and an object side lens surface78 a of the image side lens 78, which constitute cemented surfaces ofthe cemented lens, have the same shape. The object side lens 77 and theimage side lens 78 are bonded by a resin adhesive, but there isessentially zero gap between the object side lens 77 and the image sidelens 78.

When the F number of the imaging lens 70 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=88.6°

L=12.499 mm

When f is the focal point distance of the entire lens system, f1 is thefocal point distance of the first lens 71, f2 is the focal pointdistance of the second lens 72, f3 is the focal point distance of thethird lens 73, f4 is the focal point distance of the fourth lens 74, f41is the focal point distance of the object side lens 77, and f42 is thefocal point distance of the image side lens 78, these values are asfollows.

f=1.444 mm

f1=−6.918 mm

f2=−2.422 mm

f3=3.349 mm

f4=3.215 mm

f41=−3.243 mm

f42=1.752 mm

In the imaging lens 70 of the present example, when Sg1H is the amountof sag in the image side lens surface 77 b of the object side lens 77 atheight H in the effective diameter of the image side lens surface 77 bof the object side lens 77 in a direction orthogonal to the optical axisL7, Sg2H is the amount of sag in the object side lens surface 78 a ofthe image side lens 78 at height H, Rs is the radius of curvature of theimage side lens surface 77 b of the object side lens 77, R31 is theradius of curvature of the object side lens surface 73 a of the thirdlens 73, and R32 is the radius of curvature of the image side lenssurface 73 b of the third lens 73, then the conditional expressions (2),(5), and (6) given in the description of Example 1 are satisfied. Thevalues of the conditional expressions (5) and (6) are as follows.

Sg1H≦Sg2H  (2)

−3.0≦(f41/f42)/f=−1.28−1.5  (5)

R31=2.400≦|R32|=|−8.121|  (6)

Furthermore, in the imaging lens 70 of the present example, the Abbenumber of the first lens 71, the second lens 72, and the image side lens78 is 40 or greater, and the Abbe number of the third lens 73 and theobject side lens 77 is 31 or less, whereby chromatic aberration iscorrected.

In the imaging lens 70, Rs/f is equal to 0.848, which falls below thelower limit of conditional expression (4).

Next, table 6A shows lens data of the lens surfaces of the imaging lens70. In table 6A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 75, and surfaces 11 and 12 are the objectside glass surface and the image side glass surface of the plate glass76. Radius of curvature and gap are in units of millimeters.

TABLE 6A Radius of Nd (ref. Vd (Abbe Surface Curvature Gap index) no.)1  22.729 1.000 1.77250 49.6 2  4.244 1.568 3* 39.094 0.982 1.53461 56.04* 1.242 1.159 5* 2.400 1.439 1.58246 30.1 6* −8.121 0.982 7  infinity0.253 0.253 8* 3.497 0.500 1.63494 24.0 9* 1.224 1.613 1.53461 56.0 10* −2.158 1.000 11  infinity 0.700 1.51680 64.2 12  infinity 1.303

Next, table 6B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 6B as well.

TABLE 6B 3rd 4th 5th 6th 8th 9th 10th surface surface surface surfacesurface surface surface K   0.00000E+00 −1.10386E+00 −2.85133E+00  0.00000E+00   4.41585E+00 −4.03391E−01 −4.40846E−01 A4 −7.22684E−04  9.69822E−03   1.85742E−02   2.04844E−02 −1.30111E−02   3.93057E−02  1.42869E−02 A6   1.99874E−05   2.41562E−03   4.74678E−03   1.76868E−04−9.10184E−03 −6.30264E−02   2.13805E−03 A8   3.95429E−06   5.68796E−04−4.47446E−04 −4.19487E−04   0.00000E+00   6.71597E−04   1.85498E−03 A10−1.77245E−07 −2.05578E−04 −2.82868E−05   1.24097E−04   0.00000E+00  7.59331E−03 −1.10425E−03 A12   0.00000E+00   0.00000E+00   9.43715E−06  0.00000E+00   0.00000E+00 −3.65218E−03 −1.28829E−04 A14   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  2.71356E−04 A16   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00

FIGS. 19A to 19D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 70. According to the imaging lens 70 of the presentexample, axial chromatic aberration is satisfactorily corrected as shownin FIG. 19A. Color bleeding is also suppressed as shown in FIG. 19B.Both axial chromatic aberration and magnification chromatic aberrationare corrected in a balanced manner in the peripheral portions as well,as shown in FIGS. 19A and 19B. Furthermore, according to the imaginglens 70 of the present example, field curvature is satisfactorilycorrected as shown in FIG. 19C.

Reference Example 2

FIG. 20 is a configuration diagram (light ray diagram) of an imaginglens of Reference Example 2. An imaging lens 80 of the present examplecomprises, in order from an object side to an image side, a first lens81 having negative power, a second lens 82 having negative power, athird lens 83 having positive power, and a fourth lens 84 havingpositive power, as shown in FIG. 20. A diaphragm 85 is disposed betweenthe third lens 83 and the fourth lens 84, and plate glass 86 is disposedon the image side of the fourth lens 84. An image-forming surface 18 isin a separate position from the plate glass 86. The fourth lens 84 is acemented lens comprising an object side lens 87 having negative powerand an image side lens 88 having positive power. An image side lenssurface 87 b of the object side lens 87 and an object side lens surface88 a of the image side lens 88, which constitute cemented surfaces ofthe cemented lens, have the same shape. The object side lens 87 and theimage side lens 88 are bonded by a resin adhesive, but there isessentially zero gap between the object side lens 87 and the image sidelens 88.

When the F number of the imaging lens 80 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=100.8°

L=13.301 mm

When f is the focal point distance of the entire lens system, f1 is thefocal point distance of the first lens 81, f2 is the focal pointdistance of the second lens 82, f3 is the focal point distance of thethird lens 83, f4 is the focal point distance of the fourth lens 84, f41is the focal point distance of the object side lens 87, and f42 is thefocal point distance of the image side lens 88, these values are asfollows.

f=1.187 mm

f1=−6.813 mm

f2=−2.080 mm

f3=3.061 mm

f4=3.238 mm

f41=−2.699 mm

f42=1.743 mm

In the imaging lens 80 of the present example, when Sg1H is the amountof sag in the image side lens surface 87 b of the object side lens 87 atheight H in the effective diameter of the image side lens surface 87 bof the object side lens 87 in a direction orthogonal to the optical axisL8, Sg2H is the amount of sag in the object side lens surface 88 a ofthe image side lens 88 at height H, Rs is the radius of curvature of theimage side lens surface 87 b of the object side lens 87, R31 is theradius of curvature of the object side lens surface 83 a of the thirdlens 83, and R32 is the radius of curvature of the image side lenssurface 83 b of the third lens 83, then the conditional expressions (2),(4), and (6) given in the description of Example 1 are satisfied. Thevalues of the conditional expressions (4) and (6) are as follows.

Sg1H≦Sg2H  (2)

0.9≦Rs/f=1.016≦1.3  (4)

R31=2.437≦|R32|=|−5.274|  (6)

Furthermore, in the imaging lens 80 of the present example, the Abbenumber of the first lens 81, the second lens 82, and the image side lens88 is 40 or greater, and the Abbe number of the third lens 83 and theobject side lens 87 is 31 or less, whereby chromatic aberration iscorrected.

In the imaging lens 80, (f41/f42)/f is equal to −1.30, which exceeds theupper limit of conditional expression (5).

Next, table 7A shows lens data of the lens surfaces of the imaging lens80. In table 7A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 85, and surfaces 11 and 12 are the objectside glass surface and the image side glass surface of the plate glass86. Radius of curvature and gap are in units of millimeters.

TABLE 7A Nd Vd Radius of (ref. (Abbe Surface Curvature Gap index) no.)1  12.581 0.875 1.77250 49.6 2  3.598 2.342 3* −118.176 1.152 1.5346156.0 4* 1.126 1.259 5* 2.437 1.368 1.58246 30.1 6* −5.274 0.673 7 infinity 0.420 8* 4.645 0.438 1.63494 24.0 9* 1.206 1.858 1.53461 56.010*  −1.897 1.000 11  infinity 0.700 1.51680 64.2 12  infinity 1.219

Next, table 7B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 7B as well.

TABLE 7B 3rd 4th 5th 6th 8th 9th 10th surface surface surface surfacesurface surface surface K   0.00000E+00 −1.13533E+00 −4.01872E+00  0.00000E+00   5.79883E+00 −4.07305E−01 −1.94772E−01 A4 −8.54655E−04  1.39815E−02   2.10044E−02   1.45092E−02 −2.47392E−02   1.81021E−02  2.02986E−02 A6   3.48800E−06   3.24264E−03   4.34476E−03 −3.69268E−03−3.33467E−03 −7.87518E−02 −1.42584E−03 A8 −1.66300E−06   2.03665E−03−1.10311E−03   3.93990E−04   0.00000E+00   9.40828E−03   4.08231E−03 A10−1.82690E−08 −6.85755E−04 −1.91464E−05 −3.15360E−05   0.00000E+00  1.13729E−02 −2.37074E−03 A12   0.00000E+00   0.00000E+00 −3.53083E−06  0.00000E+00   0.00000E+00 −4.88917E−03   7.85272E−04 A14   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00−1.01850E−04 A16   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00

FIGS. 21A to 21D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 80. According to the imaging lens 80 of the presentexample, axial chromatic aberration is satisfactorily corrected as shownin FIG. 21A. Color bleeding is also suppressed as shown in FIG. 21B.Both axial chromatic aberration and magnification chromatic aberrationare corrected in a balanced manner in the peripheral portions as well,as shown in FIGS. 21A and 21B. Furthermore, according to the imaginglens 80 of the present example, field curvature is satisfactorilycorrected as shown in FIG. 21C.

Reference Example 3

FIG. 22 is a configuration diagram (light ray diagram) of an imaginglens of Reference Example 3. An imaging lens 90 of the present examplecomprises, in order from an object side to an image side, a first lens91 having negative power, a second lens 92 having negative power, athird lens 93 having positive power, and a fourth lens 94 havingpositive power, as shown in FIG. 22. A diaphragm 95 is disposed betweenthe third lens 93 and the fourth lens 94, and plate glass 96 is disposedon the image side of the fourth lens 94. An image-forming surface 19 isin a separate position from the plate glass 96. The fourth lens 94 is acemented lens comprising an object side lens 97 having negative powerand an image side lens 98 having positive power. An image side lenssurface 97 b of the object side lens 97 and an object side lens surface98 a of the image side lens 98, which constitute cemented surfaces ofthe cemented lens, have the same shape. The object side lens 97 and theimage side lens 98 are bonded by a resin adhesive, but there isessentially zero gap between the object side lens 97 and the image sidelens 98.

When the F number of the imaging lens 90 of the present example is Fno,the half angle of view is ω, and the entire length of the lens system isL, these values are as follows.

Fno=2.0

ω=97.6°

L=15.633 mm

When f is the focal point distance of the entire lens system, f1 is thefocal point distance of the first lens 91, f2 is the focal pointdistance of the second lens 92, f3 is the focal point distance of thethird lens 93, f4 is the focal point distance of the fourth lens 94, f41is the focal point distance of the object side lens 97, and f42 is thefocal point distance of the image side lens 98, these values are asfollows.

f=1.149 mm

f1=−8.499 mm

f2=−2.585 mm

f3=3.991 mm

f4=3.208 mm

f41=−3.508 mm

f42=1.833 mm

In the imaging lens 90 of the present example, when Sg1H is the amountof sag in the image side lens surface 97 b of the object side lens 97 atheight H in the effective diameter of the image side lens surface 97 bof the object side lens 97 in a direction orthogonal to the optical axisL9, Sg2H is the amount of sag in the object side lens surface 98 a ofthe image side lens 98 at height H, Rs is the radius of curvature of theimage side lens surface 97 b of the object side lens 97, R31 is theradius of curvature of the object side lens surface 93 a of the thirdlens 93, and R32 is the radius of curvature of the image side lenssurface 93 b of the third lens 93, then the conditional expressions (2)and (4) to (6) given in the description of Example 1 are satisfied. Thevalues of the conditional expressions (4) to (6) are as follows.

Sg1H≦Sg2H  (2)

0.9≦Rs/f=1.110≦1.3  (4)

−3.0≦(f41/f42)/f=−1.67≦−1.5  (5)

R31=3.342≦|R32|=|−5.935|  (6)

Furthermore, in the imaging lens 90 of the present example, the Abbenumber of the first lens 91, the second lens 92, and the image side lens98 is 40 or greater, and the Abbe number of the third lens 93 and theobject side lens 97 is 31 or less, whereby chromatic aberration iscorrected.

Next, table 8A shows lens data of the lens surfaces of the imaging lens90. In table 8A, the lens surfaces are specified in order counting fromthe object side. Lens surfaces marked with an asterisk are aspheric.Surface 7 is the diaphragm 95, and surfaces 11 and 12 are the objectside glass surface and the image side glass surface of the plate glass96. Radius of curvature and gap are in units of millimeters.

TABLE 8A Radius of Nd (ref. Vd (Abbe Surface Curvature Gap index) no.)1  16.292 1.000 1.77250 49.6 2  4.554 2.863 3* −52.037 1.359 1.5346156.0 4* 1.432 1.602 5* 3.342 2.021 1.58246 30.1 6* −5.935 0.889 7 infinity 0.952 8* 3.437 0.500 1.63494 24.0 9* 1.275 1.790 1.53461 56.010*  −2.164 1.000 11  infinity 0.600 1.51680 64.2 12  infinity 1.057

Next, table 8B shows aspheric coefficients for stipulating the asphericshapes of the aspheric lens surfaces. The lens surfaces are specified inorder counting from the object side in table 8B as well.

TABLE 8B 3rd 4th 5th 6th 8th 9th 10th surface surface surface surfacesurface surface surface K −3.33493E−01 −1.29400E+00 −4.40184E+00  0.00000E+00   1.49298E+00 −5.08447E−01 −4.39594E−01 A4 −6.99972E−04  9.34144E−03   1.33728E−02   1.33056E−02 −1.36471E−02   6.31739E−03  2.28238E−02 A6   1.13834E−05   6.88100E−04   5.92956E−04 −2.58752E−03  1.31356E−03 −2.58752E−03 −2.73430E−03 A8   8.10438E−07   1.84424E−04−8.48007E−05   9.16595E−04   0.00000E+00 −5.29138E−03   1.36823E−03 A10−2.53050E−08 −3.12281E−05   1.84343E−05 −7.96107E−05   0.00000E+00  4.63914E−03 −1.80092E−04 A12   0.00000E+00   0.00000E+00   1.83298E−06  0.00000E+00   0.00000E+00 −1.03406E−03   4.37716E−05 A14   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00  1.66015E−05 A16   0.00000E+00   0.00000E+00   0.00000E+00  0.00000E+00   0.00000E+00   0.00000E+00   0.00000E+00

FIGS. 23A to 23D are a longitudinal aberration graph, lateral aberrationgraphs, a field curvature graph, and a distortion aberration graph ofthe imaging lens 90. According to the imaging lens 90 of the presentexample, axial chromatic aberration is satisfactorily corrected as shownin FIG. 23A. Color bleeding is also suppressed as shown in FIG. 23B.Both axial chromatic aberration and magnification chromatic aberrationare corrected in a balanced manner in the peripheral portions as well,as shown in FIGS. 23A and 23B. Furthermore, according to the imaginglens 90 of the present example, field curvature is satisfactorilycorrected as shown in FIG. 23C.

SYMBOLS

-   10, 20, 30, 40, 50 Imaging lenses-   11, 21, 31, 41, 51 First lenses-   12, 22, 32, 42, 52 Second lenses-   13, 23, 33, 43, 53 Third lenses-   14, 24, 34, 44, 54 Fourth lenses (cemented lenses)-   17, 27, 37, 47, 57 Object side lenses-   18, 28, 38, 48, 58 Image side lenses-   15, 25, 35, 45, 55 Diaphragms-   B1, B2, B3, B4, B5 Resin adhesive layers-   L1, L2, L3, L4, L5 Optical axes-   I1, 12, 13, 14, Image-forming surfaces-   60 Imaging device-   61 Image pick-up device-   61 a Sensor surface-   62 Optical filter

1. An imaging lens characterized in comprising: a first lens havingnegative power, a second lens having negative power, a third lens havingpositive power, an aperture, and a fourth lens having positive powerarranged in order from an object side toward an image side, wherein thefourth lens is a cemented lens composed of an object side lens havingnegative power and an image side lens having positive power, the objectside lens and the image side lens each having a cemented surface that isan aspheric surface being convex toward the object side, and thefollowing conditional expressions (1) and (2) are satisfied:0.9≦Rs/f  (1)R31≦|R32|  (2), where Rs represents a radius of curvature of the imageside lens surface of the object side lens, f represents a focal pointdistance of an entire lens system, R31 represents a radius of curvatureof the object side lens surface of the third lens, and R32 represents aradius of curvature of an image side lens surface of the third lens. 2.The imaging lens according to claim 1, characterized in that thefollowing conditional expression (3) is satisfied:0.847≦f≦1.248  (3).
 3. The imaging lens according to claim 1,characterized in that the following conditional expression (4) issatisfied:0.934≦Rs≦1.398  (4).
 4. An imaging lens characterized in comprising: afirst lens having negative power, a second lens having negative power, athird lens having positive power, an aperture, and a fourth lens havingpositive power arranged in order from an object side toward an imageside, wherein the fourth lens is a cemented lens composed of an objectside lens having negative power and an image side lens having positivepower, the object side lens and the image side lens each having acemented surface that is an aspheric surface being convex toward theobject side, the following conditional expression (1) is satisfied:0.9≦Rs/f  (1), where Rs represents a radius of curvature of the imageside lens surface of the object side lens and f represents a focal pointdistance of an entire lens system, and the imaging lens has a half angleof view of 96° or greater.
 5. The imaging lens according to claim 4,characterized in that the following conditional expression (3) issatisfied:0.847≦f≦1.248  (3).
 6. The imaging lens according to claim 4,characterized in that the following conditional expression (4) issatisfied:0.934≦Rs≦1.398  (4).
 7. An imaging lens characterized in comprising: afirst lens having negative power, a second lens having negative power, athird lens having positive power, an aperture, and a fourth lens havingpositive power arranged in order from an object side toward an imageside, wherein the fourth lens is a cemented lens composed of an objectside lens having negative power and an image side lens having positivepower, the object side lens and the image side lens each having acemented surface that is an aspheric surface being convex toward theobject side, and the following conditional expressions (1) and (3) aresatisfied:0.9≦Rs/f  (1)0.847≦f≦1.248  (3), where Rs represents a radius of curvature of theimage side lens surface of the object side lens and f represents a focalpoint distance of an entire lens system.
 8. An imaging lenscharacterized in comprising: a first lens having negative power, asecond lens having negative power, a third lens having positive power,an aperture, and a fourth lens having positive power arranged in orderfrom an object side toward an image side, wherein the fourth lens is acemented lens composed of an object side lens having negative power andan image side lens having positive power, the object side lens and theimage side lens each having a cemented surface that is an asphericsurface being convex toward the object side, the following conditionalexpression (2) is satisfied:R31≦|R32|  (2), where R31 represents a radius of curvature of the objectside lens surface of the third lens, and R32 represents a radius ofcurvature of an image side lens surface of the third lens, and theimaging lens has a half angle of view of 96° or greater.
 9. The imaginglens according to claim 8, characterized in that the followingconditional expression (3) is satisfied:0.847≦f≦1.248  (3), where f represents a focal point distance of anentire lens system.
 10. The imaging lens according to claim 8,characterized in that the following conditional expression (4) issatisfied:0.934≦Rs≦1.398  (4), where Rs represents a radius of curvature of theimage side lens surface of the object side lens.
 11. An imaging lenscharacterized in comprising: a first lens having negative power, asecond lens having negative power, a third lens having positive power,an aperture, and a fourth lens having positive power arranged in orderfrom an object side toward an image side, wherein the fourth lens is acemented lens composed of an object side lens having negative power andan image side lens having positive power, the object side lens and theimage side lens each having a cemented surface that is an asphericsurface being convex toward the object side, and the followingconditional expressions (2) and (3) are satisfied:R31≦|R32|  (2)0.847≦f≦1.248  (3) where R31 represents a radius of curvature of theobject side lens surface of the third lens, R32 represents a radius ofcurvature of an image side lens surface of the third lens, and frepresents a focal point distance of an entire lens system.
 12. Animaging lens characterized in comprising: a first lens having negativepower, a second lens having negative power, a third lens having positivepower, an aperture, and a fourth lens having positive power arranged inorder from an object side toward an image side, wherein the fourth lensis a cemented lens composed of an object side lens having negative powerand an image side lens having positive power, the object side lens andthe image side lens each having a cemented surface that is an asphericsurface being convex toward the object side, and the followingconditional expressions (2) and (4) are satisfied:R31≦|R32|  (2)0.934≦Rs≦1.398  (4), where R31 represents a radius of curvature of theobject side lens surface of the third lens, R32 represents a radius ofcurvature of an image side lens surface of the third lens, and Rsrepresents a radius of curvature of the image side lens surface of theobject side lens.